Illustrated in FIG. 1 is an example application of this type of communication. A computer 11 (or a server or other) is connected for example to the power grid by a power-line communication device 10 (or to an Ethernet network via an Ethernet cable). The computer 11 is also connected to a wide area network such as the Internet 12. The computer 11 can thus connect to the Internet for a particular service (presentation of web pages or other service) and, upon receipt of these service data, send them to the device 10. The computer 11 indicates in particular the IP address of a device 14 having one or more LED (light-emitting diode) bulbs 141, 142, 143 and a Li-Fi router 13 connected to device 10 transmits these data to transmission device 14. For example, these bulbs emit light in the visible spectrum, in accordance with IEEE 802.15.7® (2011).
The device 14 is equipped with a digital encoder that allows it to transmit the information received and to modulate it (or demodulate it, particularly in the case where the device 14 comprises photoreceptors for receiving light signals from the terminals D1, D2, D3). The electrical pulses received between the router 13 and the device 14 are then converted into light pulses (or vice versa). In the example shown in FIG. 1, the device 14 comprises a plurality of bulbs that simultaneously emit the same light beam, turning on and off at a very high frequency (beyond the persistence of vision). For decoding the data thus received, the terminals D1, D2, D3, placed under the light beam, are equipped with a photodetector coupled to an integrated digital demodulator.
Each of the terminals D1, D2, D3 (smart phone, tablet, or other devices) thus receives the same data from the computer 11. However, some terminals (D1, D2, for example) may be subscribing to specific services, and others (D3) are not. It is then necessary to distinguish between the different content to be communicated to different terminals, by different respective bulbs.
Furthermore, to receive these data (or more generally simply to access the Internet upon request), these terminals D1, D2, D3 must be located within the illuminated area covered the bulbs. No possibility for mobility for the users of such terminals is provided. Specifically, if a terminal D3 moves from an area covered by device 14 to an area covered by device 15 of FIG. 1, in principle the terminal is expected to repeat an authentication procedure (and to do so systematically with each change of transmission device during its movement, from 15 to 16, etc.).
The present invention improves the situation.